Mapping columns directly to the attribute names
In the below example, the column mapping is done by mapping each of the table columns as class attributes. Each of the attributes is provided with the same name as the corresponding table columns that it represents. We then establish the SQLAlchemy engine connected to the sakila database in MySQL. Then a session object is created to query the database. Using this session object, we will query the first record in the `actor` table. We get the value of the column `first_name` for the first record by accessing the `first_name` attribute of the `result` object. This shows that the column of the actor table is mapped against the attributes of the Actor class.
Python3
import sqlalchemy as db from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() # MAPPING TABLE ACTOR class Actor(Base): __tablename__ = 'actor' actor_id = db.Column(db.SmallInteger, autoincrement = True , primary_key = True ) first_name = db.Column(db.String( 45 ), nullable = False ) last_name = db.Column(db.String( 45 ), nullable = False ) last_update = db.Column(db.TIMESTAMP, nullable = False ) # DEFINE THE ENGINE (CONNECTION OBJECT) engine = db.create_engine( "mysql+pymysql://root:password@localhost/sakila" ) # CREATE A SESSION OBJECT TO INITIATE QUERY IN DATABASE from sqlalchemy.orm import sessionmaker Session = sessionmaker(bind = engine) session = Session() # SELECT * FROM sakila.actor LIMIT 1; result = session.query(Actor).first() # DISPLAY FIRST NAME OF FIRST RECORD IN ACTOR TABLE print ( "First Name (Record 1):" , result.first_name) |
Output:
First Name (Record 1): PENELOPE
SQLAlchemy – Mapping Table Columns
In this article, we will see how to map table columns using SQLAlchemy in Python.
You will need a database (MySQL, PostgreSQL, SQLite, etc) to work with. Since we are going to use MySQL in this post, we will also install a SQL connector for MySQL in Python. However, none of the code implementations changes with change in the database except for the SQL connectors.
pip install pymysql
We will use the sample sakila database from MySQL. All the examples covered in this article will make use of the actor table within the sakila database. If you do not have the sakila database and want to follow along with this article without installing it then use the SQL script present in the link mentioned below to create the required schema and actor table along with the records.
Databased Used: Sakila Actor Table Script
We will be referring to the same SQL query in each of the examples mentioned below –
SELECT first_name FROM sakila.actor LIMIT 1;
The different ways in which we can map the columns in SQLAlchemy are –
- Mapping columns directly to the attribute names
- Mapping columns distinctly from attribute names
- Mapping columns using reflection
- Mapping columns using a prefix
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